TOKYO, Nov 21 (Reuters) - Advertising company WPP PLC has agreed to a $1.35 billion tender offer from Bain Capital LLC for Japanese peer Asatsu-DK Inc, of which it owns 25 percent, an about-face that heralds an end to a soured partnership.

A draft statement from Bain seen by Reuters on Tuesday showed WPP had agreed to the offer it initially rejected last month. Bain and WPP told Reuters on Tuesday that no agreement had been signed. They declined to comment further.

The tender offer was scheduled to close on Tuesday, but the draft statement showed Bain had extended the offer until Dec. 6.

ADK shares jumped more 5 percent to 3,660 yen on Tuesday as investors bet on the likelihood of the tender offer succeeding.

ADK had asked WPP to sell its stake to the U.S. private equity firm, to end a two-decade alliance which ADK said failed to produce synergy. But London-based WPP objected to the price Bain offered, saying the deal undervalued its business partner.

WPP sought a higher offer and this month filed for arbitration, seeking a declaration that ADK's planned termination of their business alliance was invalid, and that ADK had no right to request or require WPP to sell its shares.

But the draft statement showed WPP would withdraw arbitration and injunction proceedings if the tender offer succeeds. It did not detail reasons for WPP's change of position.

WPP also agreed to sell its ADK stake to Bain for 3,660 yen ($32.54) per share, unchanged from the initial offer, the draft statement showed.

Other ADK shareholders such as London-based fund manager Silchester International Investors LLP and Hong Kong-based activist hedge fund Oasis Management Co Ltd have also said Bain's offer was too low.

ADK and Oasis declined to comment. Silchester could be reached for comment.